1. Field of the Invention
This invention relates generally to an alternating current generating device, and more particularly to an alternating current generating device for producing a low frequency output of, for example, 50 Hz, 60 Hz, etc., wherein an inductor-type high frequency generator is used and a high frequency output thereof is rectified and combined after polarity reversion to obtain a high power low frequency output.
2. Description of the Prior Art
When an ordinary AC generator is used to obtain a low frequency output of, for example, 50 Hz, the number of revolution N of the AC generator is generally expressed by the following equation. EQU N = 120f/P (1)
where f is a frequency and P is the number of magnetic poles. In this equation, the number of revolution N is limited to 3,000 rpm even when the number of magnetic poles P is set at the minimum of two poles. For this reason, in designing, for example, a small-sized engine generator, there has been a limitation which makes it impossible to increase the number of revolution to obtain high output.
To overcome this, a technique has been developed in which two inductors whose number of teeth (poles) is slightly different from each other are used in an inductor-type generator to produce a high frequency output containing beats corresponding to the difference in the number of teeth, the positive and negative polarity portions of the envelope waveform (beat frequency waveform) of the high frequency output are separately rectified and extracted, and then superposed to obtain a low frequency output of a beat frequency of, for example, 50 Hz. In obtaining a low frequency output of, for example, 50 Hz, suppose the number of teeth in the two inductors are P1 = 12 and P2 = 11, respectively, and the frequencies of the high frequency outputs in each inductor to produce beats are f1 = 600 Hz and f2 = 550 Hz, respectively, then the number of revolution N can be set at N = 6,000 rpm, and accordingly a low frequency output of sufficient power can be obtained.
In the above-mentioned technique, however, not only two inductors having different numbers of teeth have to be provided in a high frequency generator, but the phase of the envelope waveform of the high frequency output is required to be accurately matched with the phase of the control signal for the means for separately rectifying and extracting the positive and negative polarity portions of the envelope. When the rectifying and extracting means is constructed by an SCR, for example, a circuit is required for synchronization controlling the oscillation circuit, which generates SCR trigger pulses, by means of the envelope of high frequency output of the generator. This inevitably makes the generating device of complicated construction and expensive in cost, and causes many troubles.